Method for diagnosing an exhaust gas post-treatment

ABSTRACT

Method for the on-board diagnosis of an exhaust gas post-treatment device for a combustion engine, wherein the exhaust gas post-treatment device has means for converting an exhaust gas component and wherein sensor means are provided downstream of the exhaust gas post-treatment device, wherein the exhaust gas component is acquired by the sensor means and that by means of the quantity of the acquired exhaust gas component the quality of the means for converting the exhaust gas component is derived, wherein a signal of the sensor means is transmitted to a system for the on-board diagnosis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of German Patent Application No. 102011000153.0 filed on Jan. 14, 2011, which is incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The invention relates to a method for the on-board diagnosis of an exhaust gas post-treatment device for a combustion engine, wherein the exhaust gas post-treatment device has means for converting an exhaust gas component and wherein sensor means are provided downstream of the exhaust gas post-treatment device.

BACKGROUND OF THE INVENTION

The State of the Art is, that a carbon particle filter stores soot in the so-called adsorption operation. Carbon particle filters are also called Diesel particulate filters (DPF). When the particle filter cannot absorb any further soot, it has to be cleaned by a regeneration. For this, different measures are available, whereof one is, for example, to additionally heat the exhaust gas by corresponding measures, so that the soot burns-off in the filter with oxygen contained in the lean exhaust gas. This soot burning is mostly incomplete, i.e. products of an incomplete burning, for example carbon monoxide, are produced. Furthermore, it belongs to the State of the Art, that the particle filter is catalytically coated, whereby the carbon monoxide is oxidised to a very large extent to carbon dioxide, so that the carbon monoxide behind the filter emission is very low during a regeneration phase of the particle filter. Problems arise from the fact, that this catalytic layer ages within the particle filter, so that it becomes inactive and a conversion of the carbon monoxide, produced by the regeneration, is not ensured anymore. This ageing process of the catalytic coating and the, thus, increased carbon monoxide emission during the regeneration of the particle filter is in practice a not directly recognisable problem.

DE 10 2007 009 873 A1 discloses a method for detecting the occurrence of cross sensitivities of an exhaust gas sensor. The method is used in Diesel engines, which have in their exhaust-system branch an oxidising catalyst, a particulate filter and a particle sensor. It is provided, to conclude a defect of the catalyst concerning its ability in converting a second exhaust gas component by means of operational or specifically carried-out variations of the concentration of this second exhaust gas component upstream of the catalyst. It should enable, to recognise the presence of non-converted exhaust gas components in the area of the exhaust gas sensor and if necessary to carry out a corresponding correction of the sensor signal.

SUMMARY OF THE INVENTION

It is object of the present invention to diagnose the effectiveness of the catalytic coating of particle filters.

The object is solved by a method for the on-board diagnosis of an exhaust gas post-treatment device for a combustion engine, wherein the exhaust gas post-treatment device comprises means for converting an exhaust gas component and wherein sensor means, arranged downstream of the exhaust gas post-treatment device, are provided, wherein the exhaust gas component is acquired by the sensor means and that by means of the quantity of the detected exhaust gas component, the quality of the means for converting the exhaust gas component is determined, wherein a signal of the sensor means is transmitted to a system for the on-board diagnosis. Thus, a method is provided in an advantageous manner, in which the presence or the missing of the relevant exhaust gas component can be detected. In an exhaust gas post-treatment device, working efficiently, and with correspondingly effective means for converting the relevant exhaust gas component, which, if at all, is only present in very low concentrations, it can be determined, that the means for converting this exhaust gas component operate efficiently. If on the other hand a distinctly increased concentration of the relevant exhaust gas component is measured by the sensor means, this is an indication, that the means for converting the exhaust gas component are faultily operating or are defective. Especially, in this case, a comparison with a reference value, for example, of a correctly working exhaust gas post-treatment device can be provided, which is taken as reference. If the value is larger than the reference value, it can be determined that the means for converting the exhaust gas component are faulty.

According to the invention it is provided, that the exhaust gas post-treatment device comprises at least one carbon particle filter with a catalytic coating for converting the exhaust gas component, wherein a regeneration of the exhaust gas post-treatment device is carried out, during which the exhaust gas component is produced. Of advantage is, that the function of filtering and the function of converting is combined into one component, which is available on the market in different configurations. It is also advantageous, that the carbon particle filter, which contains also the catalytic coating for converting the exhaust gas component, converts the exhaust gas components, produced during the regeneration phase.

As individual method steps it can be provided, that the exhaust gas component is acquired over a time interval, which extends from a first point in time during the starting phase of the regeneration at least up to a second point in time during the regeneration, preferably, at the end of the regeneration. In this case, it can be provided, that the first point in time coincides with the starting of the regeneration or can be after the start of the regeneration. If the first point in time coincides with the start of the regeneration, this has the advantage of a simple starting condition. Generally, the start of the regeneration is carried out by measures inside the engine like throttling, later injection timing, additional and/or later injection. Intentionally, non-combusted fuel amounts reach the oxidation catalyst. Because of the thus forced reactions in the oxidation catalyst, the exhaust gas temperature increases up to approximately 620° C. to 630° C. inside the same, however, only with some time delay to the start of the measures inside the engine. During this time interval, a breakthrough or a slippage of the exhaust gas component, not converted by the oxidation catalyst, can take place. Only after the oxidation catalyst has been heated up to an exhaust gas temperature of approximately 620° C. to 630° C., this exhaust gas component is converted. This can be designated as the end of the starting phase. The heated exhaust gas starts then the burning-off procedure of the carbon-particulates in the particle filter. To not determine this portion of the non-converted exhaust gas component, the first point in time of the measurement can be later than the starting of the regeneration by means of the sensor means arranged downstream of the particle filter. As a release condition for the temporal determination of this point in time relative to the starting of the regeneration, the temperature of the exhaust gas behind the oxidation catalyst can be used.

As the first point in time is set before the start of the regeneration, it is ensured, that the relevant exhaust gas component, if it is already emitted by the combustion engine, but has not been converted by an oxidation catalyst arranged upstream, can already be detected concerning its concentration. This can be used at a later point in time as a correction factor.

In detail it is provided, that the exhaust gas component is carbon monoxide, which content is determined by the carbon monoxide sensor. As already explained above, this is a product of the generally incomplete burning of the carbon-particulates during the regeneration phase. In a functionally effective catalytic coating of the particle filter, carbon monoxide oxidises to carbon dioxide. By the carbon monoxide sensor it can directly be determined, how high the concentration of the exhaust gas component, carbon monoxide, is during a regeneration phase of the particle filter, i.e. how much carbon monoxide is not effectively converted to carbon dioxide.

Preferably, it is provided, that, when exceeding a threshold of the quantity of the exhaust gas component, a signal of the sensor means is transmitted to a system of an on-board diagnosis (OBD). Preferably, the signal of the sensor means, which are, preferably, formed as a carbon monoxide sensor, represents the quantity, the concentration or the amount of the non-converted exhaust gas component in the total exhaust gas flow behind the filter. Thus, it is ensured in an advantageous manner, that during the operation control lights—malfunction indicator light MIL—can then be activated and the causing malfunction can be recorded.

Furthermore, the object is solved by a device for the on-board diagnosis of an exhaust gas post-treatment device for a combustion engine, wherein the exhaust gas post-treatment device comprises means for converting an exhaust gas component and wherein sensor means are provided, and the sensor means are arranged downstream of the exhaust gas post-treatment device to determine an incomplete conversion of the exhaust gas component by means of detecting the same, and wherein the sensor means are connected to a system for the on-board diagnosis.

According to the invention it is provided, that the exhaust gas post-treatment device has at least one carbon particle filter with a catalytic coating for converting the exhaust gas component. In this case, it is advantageous, that the function of filtering and the function of converting are combined in one component.

In a preferred embodiment it is provided, that the sensor means comprise a carbon monoxide sensor. By means of the carbon monoxide sensor, it can be directly determined, how high the concentration of the exhaust gas component carbon monoxide is during a regeneration phase of the particle filter, i.e. how much carbon monoxide was not effectively converted into carbon dioxide.

Alternatively, it can be provided, that the sensor means for measuring carbon monoxide are adapted from a lambda-sensor, a NOx-sensor or an electro-chemically operating sensor. Thus, the advantage is achieved, that these sensors are available on the market in many types, as they have already been used in the surroundings of an exhaust-system branch.

As a further alternative, it can be provided, that the sensor means comprise a catalytic coating and a temperature sensor. In this embodiment the detection of the exhaust gas component carbon monoxide, as far as this is not converted because of a defective catalytic coating within the particle filter, such, that the carbon monoxide, which leaves the particle filter in a non-converted condition, is followingly converted in the catalytic coating of the sensor means, arranged behind, and, in this case, causes an increase in temperature, which is detected by the temperature sensor.

For each of the embodiments it can be provided, that the sensor means are connected to a system for the on-board diagnosis (OBD). Thus, it is ensured in an advantageous manner, that during the operation, control lights—malfunction indicator light MIL—can then be activated and the causing malfunction can be recorded.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the method according to the invention and the device for diagnosing the ability of converting of a carbon particles filter by means of carbon monoxide measurement is described by using the figures. It shows:

FIG. 1 is a principal representation of an exhaust-system branch;

FIG. 2 a is a temperature gradient of a carbon particle filter with a phase of regeneration;

FIG. 2 b is the carbon monoxide emissions of a carbon particle filter with catalytic coating; and

FIG. 2 c is the carbon monoxide emissions of a carbon particle filter without catalytic coating.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a principal representation of a common exhaust-system branch 6 with a combustion engine 1, which operates, for example, according to the Diesel principle, and is, when seen in flow direction A, arranged downstream of an oxidation catalyst 2, a carbon particle filter 3 and a carbon monoxide sensor 4, which is connected to a control device 5 for monitoring the sensor signals. The combustion engine can also be a lean operated Otto-engine (petrol engine). In the manner, which is not described in more detail, but generally known, the control device is at least part of a system for the on-board-diagnosis (OBD). The carbon particle filter 3 is provided with a catalytic coating on its inside, which is not shown in detail in FIG. 1 because of the principal representation.

Furthermore, a possibility for the temperature measurement can be provided downstream of the oxidation catalyst 2. Thus, a diagnosis of the oxidation catalyst 2 is achieved by evaluating a temperature gradient behind the catalyst, after emissions in the form of not-burnt-off hydrocarbon or carbon monoxide are fed upstream of the catalyst.

In FIG. 2 over the time, different temperature gradients of a carbon particle filter and of the emissions of carbon monoxide behind the filter are shown. In detail, FIG. 2 a shows a temperature gradient of a carbon particle filter across a specific time interval, within which by means of common measures a regeneration is started. A possible measure can be, to additionally heat the exhaust gas by corresponding internal engine operating conditions, so that the carbon-particulates burn-off in the filter with the oxygen contained in the lean exhaust gas. This phase of the regeneration R is visible in the temperature gradient of FIG. 2 by means of the temperature increase.

FIG. 2 b shows the carbon monoxide emissions of a carbon particle filter provided with a catalytic coating. Directly after the beginning of the regeneration, the concentration K of carbon monoxide temporarily increases, until the catalytic coating is heated-up and the carbon monoxide is oxidised to carbon dioxide. Further in FIG. 2 b, the integral I of the carbon monoxide emissions is shown.

For comparison, in FIG. 2 c the carbon monoxide emissions of a non-catalytic coated carbon particle filter are shown. In such a filter, during the regeneration R, a distinct increase of the concentration K of carbon monoxide is observed. By means of the integral I, it is shown, that a distinct larger total amount of carbon monoxide was emitted compared to a catalytic coated carbon particle filter (FIG. 2 b).

The basic idea of the method and of the device according to the invention is based on the fact, that by means of a carbon monoxide sensor downstream of the filter, the concentration of carbon monoxide can be measured in the exhaust gas flow and that a catalytic coated carbon particle filter, which coating, however, is functionally ineffective because of ageing or other damaging influencing factors, will at least generally have the concentration gradient of carbon monoxide as shown in FIG. 2 c, during the regeneration R. In this case, the carbon monoxide sensor measures during the regeneration an increased concentration of carbon monoxide. When it can be excluded, that because of other malfunctions in the exhaust-system branch 6 upstream of the carbon particle filter 3, an increased concentration of carbon monoxide is produced, it can be diagnosed, that the catalytic coating of the carbon particle filter is damaged, so that it cannot convert carbon monoxide produced during the regeneration R to carbon dioxide, and the carbon monoxide is emitted in a non-converted manner.

A possible procedure during the carrying out of the method according to the invention consists of the steps:

-   -   starting the regeneration by common measures,     -   measuring the emission of carbon monoxide,     -   integrating the emission of carbon monoxide, preferably, up to         the end of the regeneration,     -   comparing the integral of the emissions of carbon monoxide with         a reference value of a reference filter, which, preferably, is a         filter, fully functioning concerning the conversion, for example         with a conversion rate of 99%,     -   starting the measures in dependency of the value comparison,         wherein a faulty coating can be determined, when the measured         value is larger than the reference value.

As a starting measure, initially a control light (malfunction indicator light MIL) lights up for information purposes. As a further measure, the emergency operation of the combustion engine can be taken into account.

By means of the described method, it is possible to detect an ageing of the catalytic coating of a carbon particle filter. When the catalytic coating is aged, allows this again conclusions, that also the conversion of carbon monoxide (CO) and of unburnt hydrocarbon (HC) at cold temperatures, like after the cold start of the engine, can be reduced. Because of this, it is also indirectly possible by means of the method according to the invention, to diagnose also the ability to convert CO and HC during the normal operation, to which also a cold start belongs.

It is to be understood that various modifications are readily made to the embodiments disclosed herein without departing from the scope and spirit thereof. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiment, but by the scope of the appended claims. 

1. A method for the on-board diagnosis of an exhaust gas post-treatment device for a combustion engine, comprising: providing an exhaust gas post-treatment device, a means of converting an exhaust gas component and a sensor means arranged downstream of the exhaust gas post-treatment device, wherein the exhaust gas post-treatment device has at least one carbon particle filter with a catalytic coating for converting the exhaust gas component; acquiring the exhaust gas component by the sensor means and determining the quantity of the acquired exhaust gas component; determining the quality of the means for converting the exhaust gas component; transmitting a signal of the sensor means to a system for on-board diagnosis; and regenerating the carbon particle filter, during which the exhaust gas component is produced.
 2. The method according to claim 1, wherein the exhaust gas component is acquired during a time interval, which extends from a first point in time during the starting phase of the regeneration at least up to a second point in time during the regeneration.
 3. The method according to claim 2, wherein the first point in time coincides with the start of the regeneration or a time after the start of the regeneration.
 4. The method according to claim 1, wherein the exhaust gas component is carbon monoxide, which content is determined by a carbon monoxide sensor.
 5. The method according to claim 1, wherein, when exceeding a threshold value of the quantity of the exhaust gas component, a signal of the sensor means is transmitted to the system for the on-board diagnosis.
 6. A device for on-board diagnosis of an exhaust gas post-treatment device for a combustion engine comprising an exhaust gas post-treatment device for converting an exhaust gas component and a sensor, wherein the exhaust gas post-treatment device has at least one carbon particle filter with a catalytic coating for converting the exhaust gas component, the sensor means is arranged downstream of the exhaust gas post-treatment device, to detect an incomplete conversion of the exhaust gas component during a regeneration of the carbon particle filter by detecting the same, and the sensor is connected to a system for the on-board diagnosis.
 7. The device according to claim 6, wherein the sensor means has a carbon monoxide sensor.
 8. The device according to claim 6, wherein the sensor for measuring the carbon monoxide is adapted from a lambda-sensor, a NOx-sensor or an electro-chemically operating sensor.
 9. The device according to claim 6, wherein the sensor has a catalytic coating and a temperature sensor. 